1. Field of the Invention
The present invention relates to the detection of defects in a semiconductor wafer. More particularly, the present invention relates to the detecting of damage at the outer peripheral edge of the wafer before/after the wafer is processed. The present invention also relates to the inspection of a semiconductor wafer before and/or after the wafer is cleaned.
2. Description of the Related Art
In general, semiconductor devices are fabricated by selectively and repetitively subjecting a wafer to such processes as photolithography, etching, diffusion, chemical vapor deposition (CVD), ion implantation and metal evaporation processes. More specifically, the manufacturing of the semiconductor devices entails loading a plurality of wafers in a cassette, transferring the wafers to various fabricating apparatus in which the above respective processes are performed, aligning the wafers relative to the fabricating apparatus, processing the wafers in the apparatus, withdrawing the wafers from the apparatus using a robot, and then transferring the processed wafers to a predetermined position. In addition, the wafers must be placed in a stand-by state for certain amounts of time in the course of the above-described progression of respective processes.
Each wafer is also cleaned to eliminate from its surface certain substances such as foreign particles or a reactive outgrowth produced by the previous processes.
Also, only normal wafers among the respective wafers subjected to a certain unit process are allowed to proceed to the next process. Thus, inferior or damaged wafers must be detected.
Further in this respect, the edge of a wafer is typically weak and experiences many impacts with the cassette fabricating equipment. Thus, the edge of a wafer is frequently slightly damaged. However, none of the detecting apparatus are capable of discriminating such a damaged state of a wafer. As a result, wafers damaged or broken in this way are not detected and rejected but are transferred to the next process together with the normal wafers.
The damage at the edge of the wafers gradually increases due to the pressure under which the following process is carried out, the heat that is generated in the equipment or further collisions with other components of the equipment, etc. As a result, the damaged edge of the wafer breaks up into small particles. These particles can cause other wafers to become damaged and pollute the fabricating equipment. This, in turn, requires the fabricating equipment to be repaired and/or cleaned, thereby lowering the operating efficiency of the fabricating equipment.
In an attempt to overcome such problems, the outer edge of the wafer is inspected by eye or using an optical device such as a microscope. However, such inspection procedures require much working time and are not highly reliable.
Furthermore, another conventional technique to check for damage at the edge of the wafer involves irradiating the edge portion of the wafer while the wafer is rotated, detecting the intensity of the light that disperses from the edge portion of the wafer, and determining whether the wafer is damaged based on the detected intensity of the dispersed light. In this technique, the wafers must be aligned and rotated in correspondence with the irradiation of the inspection light. However, in this technique, the manner in which the wafer is supported, and the curved surface at the edge of the wafer make it difficult to measure the intensity of the dispersion light with a high degree of reliability.